Guest post by Bill DiPuccio, Science Teacher
Let’s face it, high school science videos can be boring and ineffective. I like my science with a twist of comic exaggeration. So I decided to produce a video with enough humor to keep the students awake, and enough depth to challenge them intellectually.
This 30 minute video on the Greenhouse Effect is the prototype for a possible new series: “Bill Scientific” (I gave it a personal imprint to infuse some warmth and presence). Unlike introductory videos which attempt to cover a broad field of knowledge in a short time, the goal of this prospective series is to drill down into specific, but pivotal, topics in the physical and earth sciences.
Rather than just spooning out information, each program would be designed around experiments (the simpler the better) that can be used to illuminate and verify crucial scientific principles. Students will see science in action and gain a better grasp of the empirical basis for scientific theories.
Of course, future programs will depend on the response from students, educators, and scientists, as well as securing funding. The “Greenhouse Effect” was shot and produced on amateur equipment and software. Despite these limitations, I believe the final product faithfully conveys the intent of series.
P.S. If you like the video, pass it on!
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Hi Bryan: according to tjf, the extra heat arriving by ‘back radiation’ into the inside of your coat only occurs when the sun is shining but we have to work out the thermodynamics to prove it’s true.
Have you done so? For the life of me, I can’t but probably that’s because I trained as a metallurgical engineer at Imperial College, specialising on process engineering, with a subsequent PhD in applied physics and 30 years experience running international research including CO2 related technologies.
Apparently, to really understand the new physics, you have to qualify in climate science or similar where such changes to 150 years of knowledge are proven solely by modelling!
Leonard, overall I agree with you. The radiation balance from the “top of atmosphere”, along with knowledge of the lapse rate, is probably the best way to understand “the greenhouse effect”.
If I might, I would suggest a few adjustments to what you said.
“The heat transfer rate will not change at different surface temperatures. i.e., the greenhouse induced warmer Earth does not have a different rate of heat transfer than a planet with no greenhouse effect, but with the same albedo. “
At any global temperature, the heat transfer rate is zero (to maintain the constant temperature), which is certainly constant and hence “will not change” . OTOH, specific processes can certainly change (more downward IR with more GHG, for example). When I first read your description, I thought you meant nothing changes with more GHGs, which is clearly false.
“3) The temperature gradient (average) is called the lapse rate, and only depends on the specific heat of the gas, gravity, and phase change of water vapor. ”
The “adiabatic lapse rate” is a theoretical calculation that depends on the factor you state. The actual gradient can and does vary from this value. I tried to give my own explanation of the lapse rate and its relationships to the GHE here: https://sites.google.com/site/sciencestatsandstuff/global-warming/greenhouse-effect/lapse-rate — comments welcome).
ZP … I’ll make you a bet
1) You photocopy a ruler with mm marks — any where from 90% to 110% size. Don’t tell me the scale you used.
2) You make two seperate objects about 20 cm long (give or take a cm).
I think we both agree that I will not be able to tell you the true length of either object to any better than +/- 2 cm.
I bet that I will be able to tell you the difference in length to within 0.3 cm. Would you take that bet?
Hi Mydogsgotnonose
I agree with you that you can test as to whether an energy transfer can be described as a heat transfer.
You are correct to insist that the transfer must be capable of doing thermodynamic work in the given situation
Carnot and Clausius were practical men who thought about the most efficient way to extract work from a heat engine.
They found that work (such as a moving piston output) can only be obtained with a high temperature source and a low temperature sink.
Its clear then that heat is a Macro Quantity
To test to see if an energy transfer qualifies as being HEAT.
1. For a complete cycle extract energy at a higher temperature source do work then dump unused energy to lower temperature sink.
This is a HEAT TRANSFER and happens all the time!
2. From colder to hotter object, spontaneously extract energy do work and dump unused energy to higher temperature sink NEVER HAPPENS.
So this energy transfer CANNOT be called HEAT.
So if HEAT can only BE transferred spontaneously in one direction why do some still insist in calling it NET?
However some continue to use the term NET HEAT for a two way radiative exchange.
This is wrong but understandable as climate science is in a muddle about what exactly the difference is between the terms heat, energy, work and radiation.
There is no heat transfer from colder to hotter object!
However (and this is where we may differ)
1. There is a two way radiative exchange.
2. There is a two way energy exchange.
Take 3 objects in local thermodynamic equlibrium with a vacuum separating them ;
A one at 270K
B one at 300K
C one at 330K
All three will include 10um radiation within their Planck spectrum
We are both in agreement that B can accept a 10um from C.
Some however think that B will reject an identical 10um photon from A
This makes no logical sense.
tjfolkerts 7:15 am
Your equations are correct, as far as they go. You have merely mis-applied them. Unfortunately, like all warmists, you cannot accept that in relation to the Earth, the Sun is not an internal source. It is some distance away from the Earth. To use your poor analogy about houses and furnaces, put your furnace 10 kms away from the house, and tell me how the insulation raises the temperature inside the house. Go a little further, and turn your furnace off 12 hours out of 24. Your analogy doesn’t include the Sun, so no external sunlight allowed. Hmm. Double your insulation. Hmm.
But before that, briefly explain, if you will, why the maximum temperature on the Moon (without appreciable atmosphere) exceeds that of Earth ( with atmosphere.) Ah, I see, you can’t.
Obviously, if you supply energy to a body faster than it can dissipate it, the temperature will rise. That is demonstrably not the case with the Earth. You can walk around on the solidified surface, which doesn’t even get as hot as the Moon.
I would prefer to discuss reality, but I can discuss fantasy all you want.
Live well and prosper.
Mike Flynn
Mydogsgotnonose says: April 29, 2012 at 2:16 am
SergeiMK: a bolometer is similar to a pyrgeometer in that it measures the temperature difference between a collector in radiative equilibrium with the radiator and a controlled temperature reference
A negative temperature difference means the viewed material is colder.
———
The bolometer is hotter than the object. According to you it is impossible for the cooler object to heat a warmer object.
SO
If the bolometer is at 50C then the radiation from any thing below this temperature will have no effect on it. So this would limit its use from 50C upwards. It works down to -20C.
You need to remember that the ir camera produces an image.
Heat from the bolometer will be radiated away in all directions there can be NO imaging of the object from this radiation leaving the bolometer. Radiation leaves the bolometer before it knows where it will land so will be equal from all parts of the bolometer even if it eventually lands on a cooler object beyond the lens.
Unless you postulate negative energy rays (cold rays) (this would be a new concept on me!) from the cold object that can be FOCUSED onto the bolometer then I cannot understand how your statement repeated above explains a bolometer’s operation.
If you assume normal physics applies then the thermal imaging camera can be understood.
Point the camera at 100C the bolometer receives radiation focused on it and its temperature raises above its ambient.
Point the camera at 0K the bolometer receives no radiation so will stay at its ambient.
Point the camera at -20C the bolometer receives radiation focused on it and its temperature will rise but too a lower value than in the 100C case.
A -20C object will therefore produce an image in the bolometer’s output.
“Your equations are correct, as far as they go. “
Glad we can agree on at least that much. 🙂
“But before that, briefly explain, if you will, why the maximum temperature on the Moon (without appreciable atmosphere) exceeds that of Earth ( with atmosphere.) Ah, I see, you can’t.”
I don’t know where you got the idea that this would vex me in the slightest. Incoming sunlight is ~ 1368 W/m^2. Assuming the surface of the moon or earth have an emissivity of 1 for thermal IR, the maximum temperature achievable (without mirrors or lenses or such) would be ~ 121 C. The albedo of actual rocks would lower this slightly; the emissivity of actual rocks would raise this slightly. Overall, 120 C is a pretty good approximation for high-noon on the moon.
Even on a clear day, the noon insolation at the surface of the earth is more like 1000 W/m^2 because some sunlight is absorbed/scattered before reaching the surface. This would put the high-noon temperature (due to sunlight alone) at the surface of the earth more like 90 C. There are couple adjustments to this result. Two big effects are conduction and convection, both of which serve to drain off energy, thereby lowering the temperature that can be achieved. On the other hand, there would still be some downward IR from the sky, which would add some energy. But overall, the max temperature on the earth would be less than on the moon.
That was easy. You apperently have seriously “misunderestimated” my understanding.
“you cannot accept that in relation to the Earth, the Sun is not an internal source. ”
The sun itself is clearly “external” to the earth. But (most of) the energy from the sun can easily get “inside” the boundaries of the earth (ie inside the top of the atmosphere) — about half of it even gets all the way to the surface. Once the energy is inside those boundaries, that energy is “internal”. How is this a difficult concept?
“To use your poor analogy about houses and furnaces, put your furnace 10 kms away from the house ”
Actually if you are trying the make this extension to the analogy, then put a nuclear power plant far away, and find a way to channel the EM energy generated there thru the walls of the house to the electric heater inside. (Of course, the analogy is getting terribly strained, but I am working now with your version of the analogy.)
But the simple fact is that (much) EM energy from the sun easily passes through the atmosphere (similar to the way the electrical energy passes thru the walls of the house). Once at ground level below the atmosphere, the EM energy is converted to thermal energy by a device called a “rock” (similar to the electrical energy being converted to thermal energy inside your house by a resistor).
So the analogy still sort of works. It is better in the end to discuss the actual system. But analogies can be helpful to frame the issues on more familiar settings.
###########################
Finally, the “greenhouse effect” is not about maximum temperatures, but average temperatures. Whether the high-noon moon temperature is higher than the high-noon earth temperature is immaterial. The question is “is the average temperature higher with gases that absorb and emit IR than it would be without those gases?”
“So if HEAT can only BE transferred spontaneously in one direction why do some still insist in calling it NET? …
There is no heat transfer from colder to hotter object!”
By definition, heat *is* the net transfer of energy due to a temperature difference between two objects. The net transfer must always increase entropy (or possibly keep it the same), which guarantees that more energy goes from hot to cold, than from cold to hot.
So, yes, saying “net heat” is a bit redundant, but “net thermal energy exchange” is NOT redundant.
For example, when a warmer piece of metal touches a cooler piece of metal, the transfer of energy is accomplished by collisions of atoms where they are touching. When a fast atom hits a slower atom, the fast atom tends to lose energy and the slower atom tends to gain energy. Often the faster atom is in the warmer object, but not always. Billions of times per second, collisions will transfer energy “backwards” from cooler to warmer. But when averaged out, more collision will transfer energy forward. The net transfer of energy (when averaged over billions of collisions) is always from warmer to cooler, ie the heat is from warmer to cooler.
tjfolkerts 6:34
Nearly there. But, correct me if I am wrong, you are saying that reducing the amount of energy reaching a surface by a ratio of approximately 1000/1368 will cause the average temperature of a body to rise?
You will have to excuse me for thinking that less input of energy means less input of energy. Less energy available within a body results in less EMR emission, and we use temperature as a proxy.
I am reasonably sure you cannot come up with a reasonable analogy showing that a loss of energy results in a rise in temperature.
it’s been fun, but the CO2 house of cards is approaching its “use-by date.”
Live well and prosper.
Mike Flynn.
OK — this is taking too much of my time. We have reached “hydra stage”, where two new questions pop up for everyone that is answered, and I don’t have time to keep going. A few parting comments for this thread.
1) Being careful with language is important. Unfortunately, we are fighting common usage. For example, Dictionary.com defines the verb “heat” as “to make hot or warm” (and has no definition similar to the thermodynamic definition). Since the atmosphere does help to make the surface warm, the atmosphere “heats” the surface according to this definition. But by the strict thermodynamic definition, the atmosphere definitely does not “heat” the surface.
I try to stick to the precise thermodynamic definitions, but I am sure I slip up occasionally.
2) Being able to use equations and numbers is a strong sign of understanding. If you can’t give at least a rough estimate of numbers and the equations involved, you probably don’t understand the science.
I try to give specific numbers or specific equations, so that it is easy for others to address specificis.
3) Thermodynamics is a notoriously difficult and subtle branch of physics. It requires very careful language. It requires advanced mathematics and partial derivatives. It requires the ability to calculate entropy and enthalpy and free energy. Ideally it includes knowledge of microstates and macrostates and advanced topics in probability. If you can’t apply multiple versions of the 2nd Law, then you probably don’t understand the 2nd Law.
I am sure I understand thermodynamics better than most people in this discussion, but I also know I have much more I could learn.
4) Blogs are poor places to discuss advanced science. Limitations of time, typesetting, language and common understanding doom most discussions to run around in circles.
So … enjoy the discussion. Hopefully you all will continue to learn from others and become better informed.
OK — one last comment
“But, correct me if I am wrong, you are saying that reducing the amount of energy reaching a surface by a ratio of approximately 1000/1368 will cause the average temperature of a body to rise?”
That is not quite what I was saying …
1) Reducing the input to a system (keeping other things equal) does indeed lower the temperature of a system (until a new equilibrium is reached).
2) Reducing the output (keeping the input constant) will increase the temperature (until a new equilibrium is reached).
For the system consisting of the surface of the earth (ie put an imaginary boundary right at the bottom of the atmosphere), the atmosphere does BOTH of these things. The atmosphere first reduces the input to the surface by reflecting/scattering/absorbing some sunlight. Given the amount of energy that DOES reach the ground, the atmosphere then reduces the net energy loss by providing some IR photons that get absorbed by the ground. (Fighting this effect are evaporation and convection, which INCREASE the loss from the surface).
So were are left with three cooling effects (for the earth compared to the moon) –> reduced sunlight, convection and conduction. We have one warming effect –> IR photons back from the atmosphere.
There is no a priori way to know if these will have a net warming effect (as measured by some sort of “global average temperature”). Measurements of global temperatures show the earths surface IS warmer than the moon’s surface, so experiment shows the net effect is positive. Estimations of the various effects individually seem to confirm the net effect is positive.
The REAL question is “how big of an effect will ADDITIONAL GHG’s have on the climate”. They should increase the downward IR, but they could also increase the cloud cover, thereby reducing the incoming energy. Here I don’t have a clear answer, because I don’t know enough of the details.
I really shouldn’t bother , BUT –
As you say, the atmosphere reduces input to the surface – no argument.
You go on to say that the atmosphere then ” . . . reduces the net energy loss by providing SOME . . .” (my emphasis.) – once again no argument.
Can you not see that the atmosphere making up SOME of the loss is not the same as compensating for ALL of the loss?
The warming effect from the atmosphere, as you say, does not fully compensate for the amount of radiation initially prevented from reaching the surface – I will accept your nominal 368 w/sq. m. for this purpose. The atmosphere cannot provide more than this figure to the surface (as you say, it provides some of it, not all.)
So yes, you have established that there is less energy reaching the surface than would occur without an atmosphere. I agree with your argument. No “global warming” due to CO2 whatsoever.
Given the fact we both agree that measuring the average temperature of the Earth”s surface at any point in time, the physics at least can determine whether global warming is possible given heat sources both external and internal to the lithosphere, the aquasphere and surrounding atmosphere. It is not.
Live well and prosper.
Mike Flynn.
tjfolkerts says;
” Being careful with language is important. Unfortunately, we are fighting common usage. For example, Dictionary.com defines the verb “heat” as “to make hot or warm” (and has no definition similar to the thermodynamic definition). Since the atmosphere does help to make the surface warm, the atmosphere “heats” the surface according to this definition. But by the strict thermodynamic definition, the atmosphere definitely does not “heat” the surface.”
Why is it that professionally qualified people who should know better jump on the “common usage” bandwagon instead of carefully explaining the proper physical understanding.
The ‘man in the street’ has all sorts of odd notions like;
A whale is a fish
The Sun rises in the East over a stationary Earth
The Earth is flat
Why is it that nobody suggests that because ‘we are fighting common usage’ we should accept these erroneous ideas?
.
_Jim says:
April 27, 2012 at 8:46 am
And so there you have it.
The 12 easy steps to understanding the minor but important (as to moderating the surface temperature of the earth) GHG effect.
Where’s the Water Cycle in all that?
tjfolkerts says:
April 27, 2012 at 3:39 pm
montanaconserv writes: “I have read in a few places where the GreenHouse Effect really doesn’t exist anywhere but in a greenhouse … “
One constant problem is that “the greenhouse effect” means different things to different people. I suspect it would not be difficult to find a dozen or more significantly different variations on definitions for “the greenhouse effect.” So before stating whether or not it exists, it is important to state clearly which specific version of “the greenhouse effect” you mean.
=======
The whole “the Greenhouse Effect is real” propaganda is science fraud – the warmists who claim Carbon Dioxide has The Power to raise the temperature of the Earth 33°C are in agreement that this is what is the “Greenhouse Effect”, but there’s no agreement about how it achieves this. There is ‘apparently’ no agreement on what the “Greenhouse Effect” is because there is no Greenhouse Effect. If there was the warmists would be able to explain it and the explanation would be consistent and the explanation would make physical sense.
You, generic warmists, wave generally in the direction of Tyndall who never proved that Carbon Dioxide raises the temp of the Earth 33°C and Arrhenius who misunderstood Fourier and so believed the atmosphere was like solid glass, but refuse give real science data to show how it is able to do this as you claim.
You, all warmists, are b*llsh*tt*ing.
Where’s the Water Cycle?
Bryan says:
April 29, 2012 at 3:39 pm
Hi Mydogsgotnonose
http://wattsupwiththat.com/2012/04/27/pilot-video-for-a-series-bill-scientific-the-greenhouse-effect/#comment-971089
..
I agree with you that you can test as to whether an energy transfer can be described as a heat transfer.
You are correct to insist that the transfer must be capable of doing thermodynamic work in the given situation
Carnot and Clausius were practical men who thought about the most efficient way to extract work from a heat engine.
They found that work (such as a moving piston output) can only be obtained with a high temperature source and a low temperature sink.
Its clear then that heat is a Macro Quantity
To test to see if an energy transfer qualifies as being HEAT.
1. For a complete cycle extract energy at a higher temperature source do work then dump unused energy to lower temperature sink.
This is a HEAT TRANSFER and happens all the time!
2. From colder to hotter object, spontaneously extract energy do work and dump unused energy to higher temperature sink NEVER HAPPENS.
So this energy transfer CANNOT be called HEAT.
So if HEAT can only BE transferred spontaneously in one direction why do some still insist in calling it NET?
However some continue to use the term NET HEAT for a two way radiative exchange.
This is wrong but understandable as climate science is in a muddle about what exactly the difference is between the terms heat, energy, work and radiation.
There is no heat transfer from colder to hotter object!
===============
In so much of a muddle that they claim shortwave direct from the Sun heats the land and oceans and claim that the direct heat from the Sun, thermal infrared, heat, longwave, doesn’t reach the surface and plays no part in heating land and oceans.
They have no concept of heat.
Because they have a different physical reality from the real world – they have only radiation in empty space created out of the concept of the imaginary ideal gas in a container, they do not have convection or gravity because they do not have real molecules with real weight, volume, attraction.
They have clouds in their fictional atmosphere, but they can’t explain how they got there…
This is the Greenhouse Effect explained by NASA – http://science.nasa.gov/science-news/science-at-nasa/2000/ast20oct_1/
AGWScienceFiction has shortwave visible light heating land and oceans and no heat direct from the Sun warming the land and oceans..
The heat direct from the Sun is thermal infrared, longwave. The direct heat from the Sun, the direct thermal energy of the Sun in transfer, is what directly heats the oceans and lands. NASA used to teach that it was this which warmed the Earth and us..
NASA: “Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat! The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared.
Shorter, near infrared waves are not hot at all – in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV’s remote control.”
Now NASA is pushing this fictional fisics of the Greenhouse Effect.
How anyone can take this seriously is now quite beyond my comprehension…
Please explain to me how an uncooled thermal imaging camera forms an image of objects below the ambient temperature. There must be something at -20C being focussed on the microblometer at 55C to create an image.
If it is normal physics it is LWIR heating the bolometer (cold heating hot)
If it is your physics how do you explain the -20C image?
Something must be coming through the germanium lens to be focussed on the FPA. What is it?
The camera is sensitive from 7um to 17um approx.
Mike, you are mis-interpreting the situation when you say “Can you not see that the atmosphere making up SOME of the loss is not the same as compensating for ALL of the loss?”
Suppose we start with 342 W/m^2
“Some” of the 342 makes it to the ground. Supppose that is 240 W/m^2 .
“Some” of the 240 gets returned to the surface.
* if “some of 240” = 50, then the IR return by the atmosphere doesn’t make up for the albedo loses by the atmosphere, and the surface is cooler than it would be with no atmosphere.
* if “some of 240” = 102, then the IR return by the atmosphere just makes up for the albedo loses by the atmosphere, and the surface is the same as it would be with no atmosphere.
* if “some of 240” = 150, then the IR return by the atmosphere more than makes up for the albedo loses by the atmosphere, and the surface is the warmer than it would be with no atmosphere.
This much is easy, since all the numbers are hypothetical. It is easy to come up with “some” numbers that lead to either warming or cooling.
The tougher challenge is to estimate what “some” numbers are. Trenberth made some estimates. You are welcome to argue (with numbers and calculations) where he might be off. I am satisfied that the estimates are in the in the right ballpark. The simple fact that the average temperature is above ~ 0 C means that the atmosphere does indeed have a net positive effect.
The REALLY tough challenge is to predict what the numbers would be in OTHER circumstances (for example if CO2 rises to 500 ppm). Here I don’t typically hazzard a guess, since this is pretty much a “wicked problem” http://en.wikipedia.org/wiki/Wicked_problem
tjfolkerts,
Hi.
You have started with 342 W/m^2 insolation.
You remove 102, allowing 240 to impinge on the surface.
I assume instead of “. . . returned to the surface . . .”, you meant to say “returned to the atmosphere”.
To continue. In your first case, you state that the “. . . surface is cooler than it would be with no atmosphere.” I point out that without any atmosphere, the surface would have received 342 – your figure. If you are trying to insist that that surface temperature increases when the incoming energy decreases, we both have a problem. Reducing the energy from 342 to less than 240 increases the temperature by increasing the incoming energy by reducing it?
But no matter. I may have misunderstood.
However, your second point seems to be more definite. You say 240 reaching the surface causes exactly the same result as 342 without atmosphere, which is to say 342, no more no less.
Now your last point just cannot be. Without an additional source of heat, the energy reaching the surface cannot exceed 342. That’s all there was. No amount of bouncing, absorbing, reradiating, or reflecting can increase the amount of radiation that the source emitted.
Trenberth and his motley crew might just now be accepting that they cannot find the “missing heat” because it doesn’t exist.
A common misconception is that the atmosphere (or the supposed GHGs that it contains,) somehow acts as a “one way insulator” selectively reflecting some IR wavelengths, thereby causing an elevation in surface temperatures. Now this cannot be. Suppose you choose a area of the surface such that insolation of 342 causes a temperature rise of 1K. I believe it is fair to say that if that area radiates 342 (regardless of wavelength – we are discussing energy,) then the temperature will drop by as much as it increased. Net energy change – zero.
Using your figures, 240 reaching the surface will cause a rise in temperature of xK.
Radiating 240 causes a drop in temperature of xK. Net change – precisely nil. If part of that 240 is subsequently returned to the surface, then the temperature will rise above nil in proportion to the fraction of the 240 returned, as it were. At night it will radiate that energy away.
To assume that the magical properties of global warming can somehow “reradiate” more than the 240 available is like trying to say 4=3, and then proving that 4 x 0 = 3 x 0, and cancelling out the zeros.
The other minor problems with the selective blocking, in any case, are twofold at least. We know that all visible radiation penetrates the atmosphere containing its wide variety of assorted crud,to space. Pictures of the Earth taken from space support this. Infrared, likewise penetrates rather nicely. Infrared pictures taken from space can distinguish between ice at different temperatures, so IR emitted by objects at least down to 273K travels though the atmosphere with little obstruction. Longer wavelengths, eg radio wavelengths in the SHF spectrum are bounced by amateurs using low powered transmitters off the moon and back to earth.
None of that is particularly relevant, considering that the maximum transfer of radiative energy between bodies occurs in a vacuum.
I believe we have agreed that it is impossible to measure the temperature of something that cannot even be clearly defined – the Earth’s “surface”. If anybody ever figures out a way to do it, they will find that GHGs have precisely nothing to do with any rise in temperature – apart from the heat generated in their creation.
It’s nonsense. Even you are starting to realise it’s nonsense. Join the realist club – you are most welcome.
Live well and prosper.
Mike Flynn.
ozzieostrich : April 30, 2012 at 9:38 pm
compare night and day downward IR at 2 locations:
http://www.patarnott.com/atms749/pdf/LongWaveIrradianceMeas.pdf
http://www.slf.ch/ueber/mitarbeiter/homepages/marty/publications/Marty2003_IPASRCII_JGR.pdf
Look at Upward downward spectrums for signs of GHGs wavelenghts:
http://www.patarnott.com/atms749/powerpoint/ch6_GP.ppt
Answer does a cold body heat a hot body:
See my posts above about thermal imaging cameras.
During the night solar input is zero. But downward LWIR is still within 100 watts of the upward radiation.
It is not coming from warm o2 or n2 (they do not radiate significantly). It is not coming from star/moonlight. So where do you propose this DLWIR is being sourced from.
GHGs is the answer (water vapour/co2 etc)
remember the above documents use real measured figures for IR – not models
So 2 questions:
How doe you explain the thermal imaging camera operation
What do you propose is the source of the DLWIR
Mydogsgotnonose says:
April 28, 2012 at 1:37 am
The “correct” statement would be “2 pi steradians“.
Mydogsgotnonose says:
April 28, 2012 at 2:44 pm
At night, passive solar panels radiate a lot of heat. As a result they get quite cold, much colder than the surrounding air. It is the back radiation that keeps the panels above -80°C.
Mike says: “I assume instead of “. . . returned to the surface . . .”, you meant to say “returned to the atmosphere”.
I could have been a little clearer.
* something like 342 W/m^2 of sunshine shines toward earth (when averaged over the whole surface).
* something like 100 W/m^2 of sunshine reflects/scatters back to space, without ever getting absorbed.
* something like 240 W/m^2 of sunshine gets absorbed.
* something like 240 W/m^2 of thermal IR must be generated to to conserve energy (since we know the earth is pretty close to constant temperature over long time scales). This IR shines outward away from the surface.
NOW we can look at the effect of GHGs.
* with no GHGs, all 240 W/m^2 of thermal lR will pass through the atmosphere and head away to space, never to return. 0 W/m^2 would get returned
* with a little GHG, maybe 50 W/m^2 would get returned due to IR radiation from the GHG molecules toward the surface. This would make a total of 290 W/m^2 heading down, resulting in less surface heating than a perfectly clear atmosphere.
* with a more GHG, maybe 100 W/m^2 would get returned. This would make a total of 340 W/m^2 heading down, resulting in the same surface heating as a perfectly clear atmosphere.
* with a more GHG, maybe 150 W/m^2 would get returned. This would make a total of 390 W/m^2 heading down, resulting in more surface heating than a perfectly clear atmosphere.
This all gets more complicated if evaporation and convection are included, but the principle still applies.
“the maximum transfer of radiative energy between bodies occurs in a vacuum.”
But here one of those bodies is a region of space itself! A region of the atmosphere will transfer NO radiative energy to the surface if that region is 1) a vacuum or 2) a gas with no GHGs. The transfer will increase as more GHG’s are introduced to the region (even if some of the energy is reflected/absorbed/scattered by the non-vacuum between the two. The best transfer is definitely NOT when the “body” is a region of vacuum!
“Infrared pictures taken from space can distinguish between ice at different temperatures, so IR emitted by objects at least down to 273K travels though the atmosphere with little obstruction.
Actually, only specific bands of IR can get through, and only when there is no cloud cover. The sensors have to be tuned to frequencies that are not absorbed by CO2 or H2O in order to “see” the surface. So SOME IR from the surface does get through, but most does not.
Robert Clemenzi says:
May 1, 2012 at 7:17 am (responding to)
Mydogsgotnonose says:
April 28, 2012 at 2:44 pm
I had a climate scientist argue that the reason why ‘back radiation’ did not heat up passive solar panels at night
At night, passive solar panels radiate a lot of heat. As a result they get quite cold, much colder than the surrounding air. It is the back radiation that keeps the panels above -80°C.
??????????
What (airless other world ?) location are you thinking of?
In our real world of air and wind and rain and snow and ice, the temperature of ANY exposed surface to ANY other substance (air, soil, rooftop, or solar panel mount) cannot get lower than that other surface that it touches. Thus, without laboratory conditions of artificially-driven heat exchange and artificially-applied insulation, no surface on earth can get to nor stay at -80 deg C.
Back-radiation in the real-world outdoor environment, compared to conduction and convection, is little. Not nothing mind you (see the ice forming on windshields when conduction and convection (NOTE: the windshield is HEATED by the air flow!) are changed to near-zero under clear skies and low-humidity and no wind.)
Exactly opposite your statement: Thus, it is the air flow (and its subsequent convection and conduction) NOT back-radiation that keeps exposed surfaces at night warmer than theoretical (radiation-only) models predict
Mydogsgotnonose has frequently claimed that
That is not true. Don’t confuse the absorptivity and emissivity (a function of temperature and pressure) with the energy absorbed and emitted. When the temperature is constant the amount of energy absorbed will equal the amount of energy emitted. However, the absorbed spectra and emitted spectra will be identical only at thermal equilibrium. Otherwise, the spectra will be different. That fact that the non-equilibrium spectra are different does not mean that the absorptivity and emissivity are different.